1. Field of the Invention
The present invention relates to landing gear systems used on commercial aircraft, and more particularly to an improved lower bearing assembly for the nose gear of an aircraft that provides improved wear resistance and is adapted for simple and quick replacement without requiring the aircraft to be taken out of service for extensive maintenance.
2. Description of the Background Art
The aviation industry is divided into two major providers, major air carriers and regional air carriers. The major carriers operate larger jet aircraft that are capable of transporting passengers over greater distances. These aircraft are routinely used both in intercontinental and trans-oceanic operations. The regional carriers typically provide point-to-point service on shorter routes and feeder service to their major air carrier partners through the hub and spoke transportation method. This service is accomplished through the use of smaller turbo propeller aircraft, normally ranging in size between 30 and 50 passengers.
With the increased demand on air carriers to provide more point-to-point service while improving on-time performance, the regional carriers have flourished through partnerships with major air carriers. As a result, many major carriers have signed long term contracts with regional partners on a fee per departure basis which guarantees the regional operator a fixed price every time the aircraft leaves the gate, regardless of the number of passengers actually onboard the aircraft.
The major carriers handle all of the reservation services and advertising, with the regional carriers aircraft painted to look like those of their major carrier partners. The only responsibility the regional carrier has is to make sure that the aircraft leaves the gate on time. For this their costs for operating the aircraft are covered and they are given an agreed upon profit margin, and the major carrier is responsible for filling the seats. Therefore, it has become ever more important to make sure that aircraft operated by regional carriers are capable of departing on schedule in an airworthy manner. Conversely, when the aircraft are unable to perform, the regional carrier looses money.
Most regional aircraft are designed with tricycle landing gear configuration, wherein the aircraft is equipped with a front-end or nose landing gear assembly and left and right main landing gear assemblies disposed rearward of the nose gear. During the operation of the aircraft, more specifically during take off, landing and taxiing the nose gear is subjected to loads that cause the lower bearing to become worn and loose. As depicted in FIG. 10, prior art landing gear assemblies incorporate one piece lower bearings constructed from one solid piece of 2024 T4 aluminum, a scraper ring, and an inner liner of material identified as Delrin™. The scraper ring is rubber with a metal backing for rigidity and installs into a machined mounting flange at one end of the lower bearing. The Delrin™ liner is cylindrical and split, to facilitate installation, and is inserted into the inner diameter of the lower bearing. The lower bearing is cylindrical in shape with a 90 degree retaining boss at one end with three mounting holes for bolts. This mounting flange houses the aforementioned scraper ring. The body of the lower bearing which is cylindrical in nature houses the Delrin™ liner. The aluminum lower bearing is anodized to prevent corrosion and the retaining flange is painted with a two part polyurethane paint to match that of the landing gear.
The lower bearing is installed over the outer diameter of the nose gear piston tube and into the inner diameter of the nose gear turning tube (driver). Once in this position the lower bearing is attached to the driver via three bolts that transverse through the 90 degree retaining boss and screw into corresponding threaded recesses on the driver. The inner diameter of the lower bearing has the Delrin™ segment installed and this acts as a sacrificial wear surface that comes in direct contact with the chromium finish on the outer diameter of the piston tube.
As the piston tube moves in and out of the upper bearing along its vertical axis the Delrin™ segment becomes worn. At some point, if not replaced, the Delrin™ segment can become completely worn through, leaving the chromium finish on the outer dimension of the piston tube to come in direct contact with the aluminum lower bearing. This event can cause damage to the chromium finish and can allow chromium particles to migrate up the piston tube and come in contact with the inner seal causing the nose gear to loose fluid and eventually fail.
To replace the worn or damaged lower bearing and/or the Delrin™ segment the aircraft must be brought into the hangar, elevated onto jacks and the nose gear disassembled. In order to remove the lower bearing, the nose gear must be removed from the aircraft so that a technician can gain full access to all of its components. The removal and disassembly of the nose gear can take between 6 and 8 hours with an experience crew of technicians. Once the old lower bearing was removed and a new bearing assembly is installed, the nose gear must be reassembled, tested, and finally installed on the aircraft. Once installed, final calibration and servicing of the strut is required causing additional delays. In total, an aircraft needing this type of repair would certainly be out of service for one complete day.
Accordingly, there is a need for a lower bearing that is more reliable and easier to maintain and/or replace. The lower bearing should be designed in such a manner that it provides better wear resistance characteristics and easier replacement of the main wear component. This main wear component should be able to be replaced without disassembly of the nose landing gear. The lower bearing should be designed in such a manner as to allow a technician the ability to remove and replace the main wear component while the aircraft is still located at the gate without having to raise the aircraft and/or remove the nose gear from the aircraft. It should be a process that can be accomplished in a matter of minutes, alleviating the necessity to take the aircraft back to the hangar for extensive maintenance and the cancellation of flights.